Se não houver risco de chuva, podemos fazer o churrasco no quintal.

Because after se when you are talking about a future possibility, Portuguese normally uses the future subjunctive.

So:

• Se não houver risco de chuva... = If there is no risk of rain...

Here, houver is from the verb haver, which in more formal or standard Portuguese can mean there is / there are.

Compare:

• Há risco de chuva. = There is a risk of rain.
• Se houver risco de chuva... = If there is a risk of rain...

In everyday Brazilian Portuguese, many people would also say:

• Se não tiver risco de chuva...

That is very common in speech. But houver is a standard and very natural choice, especially in writing.

Houver is the future subjunctive form of haver.

Brazilian Portuguese uses the future subjunctive a lot after words like:

• se = if
• quando = when
• assim que = as soon as
• caso = in case

It is used when the action is still uncertain or depends on something happening in the future.

So in this sentence:

• Se não houver risco de chuva...

the speaker is talking about a possible future situation, not a fact happening right now.

Yes. In Brazil, that is very common and sounds natural in conversation.

So both of these are possible:

• Se não houver risco de chuva...
• Se não tiver risco de chuva...

The difference is mostly one of style and register:

• houver sounds more standard, careful, or written
• tiver sounds more conversational and everyday

A learner should understand both.

In Portuguese, não normally goes directly before the verb it negates.

So:

• houver = there is / there will be
• não houver = there is not / there will not be

That is why the condition is:

• Se não houver risco de chuva
  = If there is no risk of rain

This word order is very standard in Portuguese.

Because de chuva here means of rain in a general sense, not of the rain referring to some specific rain.

Portuguese often uses noun + de + noun to show type, content, or association:

• risco de chuva = risk of rain
• copo de água = glass of water
• máquina de lavar = washing machine

If you said da chuva, it would sound like you were referring to some specific rain already identified in the conversation, which is not the idea here.

Because Portuguese often uses the present tense to talk about a future plan, possibility, or suggestion.

So:

• podemos fazer o churrasco
  can mean we can have the barbecue or we could have the barbecue

Even though the event is in the future, podemos sounds natural and idiomatic.

You could also say:

• poderemos fazer o churrasco

but that sounds a bit more explicitly future and sometimes slightly more formal.

In Portuguese, fazer is often used for organizing, preparing, or holding events and activities.

So:

• fazer um churrasco = have a barbecue / throw a barbecue
• fazer uma festa = have a party
• fazer um jantar = make/prepare a dinner or host a dinner

In this sentence, fazer o churrasco refers to having or holding the barbecue, not just literally making food.

Here, churrasco means the barbecue event / cookout.

In Brazilian Portuguese, churrasco can refer to:

• the style of grilled meat
• the food itself
• the social event

In this sentence, because of fazer o churrasco no quintal, it clearly means the event: having the barbecue in the yard.

Because no is a contraction of:

• em + o = no

So:

• no quintal = in the yard / in the backyard

Portuguese uses these contractions all the time:

• em + a = na
• em + os = nos
• em + as = nas

So em o quintal is not how standard Portuguese says it; no quintal is the normal form.

Not exactly.

Quintal usually means a yard, often the outdoor area of a house, especially the back part. In many contexts, backyard is a good translation.

It is not quite the same as garden in English.

Useful comparison:

• quintal = yard / backyard
• jardim = garden

So no quintal suggests the barbecue will happen in the outdoor area of the house.

Yes. You can also say:

• Podemos fazer o churrasco no quintal se não houver risco de chuva.

That has the same basic meaning.

The version with Se... first puts the condition up front:

• Se não houver risco de chuva, podemos fazer o churrasco no quintal.

This is very common because it sets the condition before the main idea.

Not exactly.

• Se não houver chuva = If there is no rain
• Se não houver risco de chuva = If there is no risk of rain

The original sentence is a bit softer and more realistic in a planning context. It is about the possibility of rain, not only actual rain.

If you are deciding whether to hold a barbecue, risco de chuva makes a lot of sense because you are looking at the forecast or chance of rain.

Yes, it is common and natural, especially in planning or weather-related contexts.

You may also hear:

• chance de chuva = chance of rain
• possibilidade de chuva = possibility of rain

These are all natural, but they can sound slightly different:

• risco de chuva often feels like there is some concern about rain
• chance de chuva sounds very similar to a weather forecast expression
• possibilidade de chuva is a bit more neutral or formal

All of them would be understandable in similar contexts.